1. Technical Field
This invention relates in general to well pumps, and in particular to a well pump housing using circulating oil to improve heat transfer.
2. Description of the Related Art
A electrical submersible pump (“ESP”) is used to pump production fluid, such as crude oil, from the depths of the earth up to the surface. The ESP is usually located in a wellbore, frequently at great depths below the surface of the earth. The ESP has a pump, a motor to drive the pump, and a seal section with a shaft between the motor and the pump. The ESP motor tends to produce heat that must be removed to prolong the life of the motor.
External devices used to decrease heat create additional costs. External cooling devices, for example, use a coolant pump above grade and coolant lines running through the wellbore to the pump. These cooling devices cool the pump by circulating the coolant through the pump and transferring the coolant back to the surface. The pump, coolant lines, and coolant all create additional costs. Furthermore, the coolant lines may interfere with well operations. The motor-pump assembly is located inside a wellbore and generally submerged in production fluid inside the wellbore so it is desirable to transfer heat to the production fluid that is flowing past the motor.
It is common to arrange the pump and motor such that the production fluid flows past the motor on its way to the pump. Heat is transferred to the production fluid and carried away as the production fluid moves to the surface. Motor oil is used inside the pump motor to lubricate the parts of the motor. The motor oil becomes hot during normal operation as it absorbs heat from the moving parts. The heat from the motor oil, like the heat from the other components in the motor, must pass through the stator and through the motor housing to be radiated to the production fluid flowing past the motor in the wellbore. It is desirable to increase the rate of heat transfer from the motor to the production fluid.